This invention relates to an apparatus for driving a moving mirror cylinder of a camera which supports a photographing lens unit and other related mechanisms, particulary an apparatus for driving the moving mirror cylinder or barrel to the first setting position located at a forward position along the optical axis or the second setting position located at the backward position along the axis
thereby to keep mechanically the setting position of the moving mirror cylinder.
When taking photographs, it is generally necessary to select a photographing lens with the most appropriate focal length that meets various types of photographers' compositions and intentions. There is a single-lens reflex camera with replaceable lenses to meet such requirements. By using such a single-lens reflex camera, almost all the compositions and intentions may be satisfied. However, a camera body is so large, and moreover the total volume become larger because an interchangeable lens must be accompanied by a lens mount and an iris-interlocking pin.
Usually, two of a wide-angle lens and a telescopic lens or two of a standard lens and a telescopic lens meet almost all the photographing requirements.
Therefore, lens shutter-type multi-focus cameras are launched on the market on the markets one after another. Generally speaking, this type of cameras incorporates a main lens system and a converter lens system in the camera body, with the main lens system being always arranged in the photographing optical axis while the converter lens system is adapted to be selectively inserted in this optical axis.
A focus distance selecting mechanism to be used in this type of multi-focus cameras is disclosed, for example, in the Japanese Opening No. 59-17540. This prior device comprises a mirror cylinder frame supported rotatably to a bearing shaft disposed along a photographing optical axis and outside an effective optical flux of the photographing optical axis, a main lens supported slidably to a camera body so as to move toward a first setting position corresponding to a wide-angle mode and toward a second setting position corresponding to a telescopic mode along an optical axis under a guide of a bearing shaft disposed on the mirror cylinder frame, and a converter lens fixed to the mirror cylinder frame and selectively inserted in the optical axis in combination with the main lens.
Therefore, the first focal length (for example, for wide-angle) of the photographing lens unit and the second focal length (for example, for telescopic) of the photographing lens are selected in the following manner:
When setting the photographing lens unit in the wide-angle mode, the main lens system is moved backward along the photographing optical axis while the converter lens is retreated from the optical axis, thereby the wideangle lens optical system is composed only of the main lens system.
When setting the photographing lens unit in the telescopic mode, the main lens system is moved forward along the photographing optical axis and the converter lens system retreated in the wide-angle mode is inserted at the rear side of the main lens system, thereby the telescopic lens optical system is composed of both the main lens and the converter lens systems.
Heretofore, those cameras which are provided with a device to electrically drive a supporting member for supporting a photographing lens unit to both first and second setting positions include, for example, a double-focus camera in which the photographing lens unit is switched to either a long focal distance side (Telescopic side) or a short focal distance side (Wide side, and a lens-projecting camera in which the photographing lens unit is housed in the front side of the camera body while it is carried (namely, while it is not in use) and is projected from the camera body when taking a photograph.
In a case where the apparatus for driving the moving mirror cylinder is adapted to support the moving mirror cylinder as the supporting member slidably at a mirror cylinder frame fixed to the camera body and to drive the moving mirror cylinder by a motor through a link mechanism, the two driving methods are conceivable to drive the said moving mirror cylinder to the said first and second setting positions.
One of the two methods is to cut off the power supply to the motor just before the moving mirror cylinder abuts against a stopper disposed at each of the first and second setting positions mounted on the cylinder frame. In this method, however, there is a problem that the stopping positions of the mirror cylinder are not stably determined due to the influences of fluctuations in the power to drive the motor and to the friction between the mirror cylinder and the cylinder frame, because the mirror cylinder abuts against the stopper only by inertia of the motor after the power supply is cut off.
The other is to cut off a power supply to the motor only after the mirror cylinder abuts against the stopper. In the latter case, however, the mirror cylinder stops while both the mirror cylinder and the cylinder frame are subjected to elastic deformation, and when the power supply to the motor is cut off, or namely when the driving force is removed, the mirror cylinder is pushed back. Therefore, there is a problem that the stopping positions of the mirror cylinder are not stable in this case, either.
FIG. 27 is a side view showing the outlined features of the apparatus for driving the moving mirror cylinder of a camera (hereinafter called a reference example).
In FIG. 27, a cylindrical moving mirror cylinder 151 supporting movably forward and backward the photographing lens unit 150 is mounted on the camera body, the lens unit 150 comprises a plurality of lenses. A flange 152 is formed at the rear end of the cylinder 151, the flange 152 is adapted to abut against the stopper 153 disposed at the camera body.
A projecting arm 152a is disposed at the rear end of the flange 152. A pin 152b is mounted on the arm 152a at an approximate center of the arm 152a.
A driving arm 154 is disposed rotatably at a bearing shaft 160 fixed to a stationary member, and a guiding hole 154c is disposed at the top end of one arm portion 154a of the arm 154. The hole 154c is oblong along a longitudinal axis of the arm portion 154a. A driving pin 158a is inserted into the hole 154c so that the arm 154 rotates around the shaft 160, as the pin 158a rotates. The base end portions of two leaf springs 154d, 154e are fixed at the top end of the other arm portion 154b of the arm 154, the top ends of two springs 154d and 154e sandwiches the pin 152b with a predetermined gap.
On the other hand, an internal gear 157 is fixed to the camera body, a smaller-diameter planet gear 158 meshing with the gear 157 is supported rotatably at a bearing shaft 159. The shaft 159 is mounted on one end of an arm section 156 the other end of which is supported rotatably around a rotating shaft 155. The pin 158a is mounted on the gear 158 apart from the center of the gear 158. The shaft 155 is connected integrally with an electric motor and a sun gear 161 meshing with the gear 158 is fixed on the shaft 155.
In order to set the cylinder 151, for example, from the long focal distance side to the short focal distance side (as shown in FIG. 27), the rotation of the motor (not shown) is transmitted to the shaft 155. Then, the gear 161 is rotated, for example, clockwise, the gear 158 revolving clockwise around the shaft 155 and rotating on its axis counterclockwise around the shaft 159. Then, the pin 158a is displaced upwards, the arm portion 154a is pushed upwards. The arm 154 rotates counterclockwise around the shaft 160, and the pin 152b is pushed by the spring 154e, thereby the cylinder 151 moves to project from the front side of the camera body. Such movement continues until the front edge of the flange 152 of cylinder 151 abuts against the stopper 153, and as the shaft 155 rotates further, the spring 154e continues to urge the pin 152b, then power supply to the electric motor is cut off. At that condition, the line connecting the center of the pin 158a, the center of the shaft 159 and the shaft 155 is aligned to the change point of the driving mechanism.
If the cylinder 151 is pressed by an external force, the cylinder 151 moves toward the long focal distance side against the force of the spring 154e. When this external force is eliminated, the flange 152 of the cylinder 151 is returned to abut against the stopper 153.
In this embodiment, however, since the springs 154d, 154e, each having a strong spring force are used to securely retain the cylinder at a predetermined setting position, a large motor torque is required to cause the springs 154d, 154e to press the cylinder 151, thereby resulting in the need of a larger-sized motor with more power consumption. Since the springs 154d, 154e, each supported like cantilever are used to retain the cylinder 151, there is a fear that the springs 154d, 154e will exceed their elastic limit and to plastically deformed if an excessive external force is applied to the cylinder 151, thereby the function to retain the setting positions is lost.
Since it is necessary to accurately set the change point in the planet gear mechanism for the purpose of assuring the maintaining of the setting positions for the cylinder 151, all the components must be machined with high precision, not leaving any unnecessary play in them, thus leading to a problem of higher machining and assembling costs.
When turning attention to a driving unit which drives the moving mirror cylinder to either the first setting position or the second setting position, the driving unit is adapted to drive the moving mirror cylinder by an electric motor via a driving system comprising a speed reduction mechanism and other components and to position the moving mirror cylinder at the first setting position or the second setting position by cutting off the power supply to the motor at the same time or immediately before an engage portion of the moving mirror cylinder abuts against stoppers disposed at portions each corresponding to the first setting position and the second setting position respectively.
When cutting off the power supply to the motor at the same time of the abuttment of the engage portion against the stopper, however, elastic deformation of the stopper or the engaging portion and the member in the driving system may cause the moving mirror cylinder to pass through the first setting position or the second setting position, and cause to return and go over the first setting position or the second setting position due to the reaction, while no external force is applied as a result of cutting off power supply to the electric motor. In other words, the moving mirror cylinder stops at a position where it is pushed back by the reaction, thereby there is a problem that the positioning of the mirror cylinder is inaccurate. To solve it, power supply to the motor is cut off immediately before the engaging portion abuts against the stopper, by anticipating the fluctuation in the stopping position of the mirror cylinder by the elastic deformation. However, an external force (driving power) is removed immediately before the abuttment of the engage portion against the stopper, thereby the movement thereafter being determined by inertia of the mirror cylinder, the driving system, and the electric motor and resulting in a problem that the performance of the electric motor, friction between the cylinder frame and the mirror cylinder, and other elements are not uniformly constant among cameras and the stopping positions of the mirror cylinder varys due to fluctuations in the power voltage of the electric motor.
The engaging portion abuts gently against the stopper rather than colliding with it by means of a chopper control system which supplys intermittent pulse-like electric power at a certain cycle and controls the pulse widths over the whole process in which the mirror cylinder is driven from the first setting position to the second setting position
However, there is a problem that the fluctuation ratio of the pulse widths cannot be uniformly determined over the whole process due to deviations of the motor performance, of friction between the cylinder frame and the mirror cylinder, and of initial location of the mirror cylinder. Conversely speaking, once the fluctuation ratio is determined, various conditions may coincide with it by chance in some cases, but the abovementioned deviations results in excessive or insufficient driving force and in an inaccurate stopping position.
Generally, a moving mirror cylinder accomodating and supporting the main lens unit therein is projects from and is to be housed to the camera body in order to change over the focal length by moving the main lens unit along the photographing optical axis. However, if dust comes in an opening between the mirror cylinder and the camera body or if an operator's (or photographer's) finger is inadvertently placed between them while the mirror cylinder is housed to the camera body from the projected condition, they will sometimes prevent the mirror cylinder from moving smoothly, thereby the mirror cylinder stopping on the way and not reaching the desired location.
Generally speaking, cameras produced in recent years adopt more electronic devices than ever, and the mirror cylinder is driven by an electric motor via a mechanical units, the position of the mirror cylinder is confirmed by means of such devices as a lens position detecting switch provided at the stop position corresponding to a predetermined focal length, and these operations are judged and controlled by a microcomputer.
If the mirror cylinder become immobile on the way to the housing position in the camera body, as described above, the microcomputer judges that the mirror cylinder does not reach the stop position because no changes are occurred in the position detecting switch, thereby the electric motor continuing to rotate. Therefore, excessive load is given to the gear system of the mechanical units, resulting sometimes in such hazards as damages in the system or injury of the operator's fingers and sometimes in a serious problem that no further photographing is possible because the mirror cylinder is not housed in the camera body. There is another defect that a large current continues to flow to the electric motor to uselessly consume the source batteries.
The power supply to the electric motor is cut off assuming that occurrence of such abnormalities is detected, if no changes are found in the position detecting switch in a predetermined time after the operation to change over the focal length (in the direction to house the mirror cylinder) is started. However, if dust or a finger is caught in an opening between the mirror cylinder and the camera body, the electric motor stops operation on the condition as it is, but in order to remove such dust or finger, the mechanical units and the motor are driven reversely. So, there is such problems as reverse driving is sometimes impossible depending on the structures of the mechanical units, and that even if it is possible, a strong external force is required for that purpose, thereby it being often seen in actuality that such dust and finger are not removed. Moreover, cameras with such a structure do nothing more than cut off the power supply to the electric motor after a predetermined time passes, and if the focal length change-over operation is started again, the electric motor is further driven in the direction to house the mirror cylinder irrespective of the fact that the mirror cylinder can not move at all.
In a variable focus optical system of the multifocus cameras, the rear surface of the lens unit is positioned near the film aperture when changing over focal lengths, if the converter lens unit is, for example, selectively inserted into the photographing optical axis. Especially in lens shutter-type cameras, it has nothing that shuts off the lens unit like a focal plane, the rearmost surface of the converter lens unit is exposed near the film aperture. On the other hand, there are general demands for more compact cameras in the markets, and in order to meet them the cameras are extremely short in back focus, namely, the distance from the apex of the rearmost surface of a photographing lens unit to the focus of an image. Since a short back focus like this causes the rearmost surface of the photographing lens unit to come immediately before the film aperture (or guide rail portion), such troubles as a photographer's finger touches the rearmost surface of the photographing lens or dust may adhere to it is not avoided, even if due care is exercised, while replacing a film or manipulating the camera by opening its rear lid. The shorter is the back focus of the photographing lens, however, the smaller is the optical flux that passes through the lens near to the film surface, and if fingerprints or dust adhere to the rearmost surface of the photographing lens, they interrupt an optical flux, often resulting in problems of uneven exposure or occurrence of flaring.
Since a photographing lens to be located near to a film is often made of plastics and is extremely soft in many cases, it is frequently damaged, if inexperienced persons attempt to wipe off the fingerprints or dust adhered as described above.
There is a possibility that a photographer's finger or foreign matter may be caught by the mechanical unit for selecting focal lengths in the conventional multi-focus cameras, thereby excessive force being applied to the mechanical unit and leading in some cases to troubles of injury or damages. Even if they are not so seriously damaged, there is a probability of degraded performance such as dislocation from the optical axis of the converter lens unit which requires accuracy.